Renal cell carcinoma (RCC) is the most common primary cancer arising from the kidney in adults, and is a frequent cause of cancer morbidity and mortality in the U.S. with over 10,000 deaths per year. Currently, there are no useful chemotherapeutic or biologic treatment modalities for patients with advanced disease.However, the biological response modifier alpha interferon (alpha-IFN) is effective in a small subset of patients. An ability to identify the subset of renal tumors sensitive to the anti- proliferative effects of alpha-IFN would clearly be advantageous as it would (i) increase the proportion of responses in patients treated with alpha-IFN; (ii) identify patients with sensitive tumors and a high risk of relapse (i.e., advanced tumor stage) for adjuvant IFN therapy; (iii) potentially provide clues for the development of new therapeutic trategies and drugs for the treatment of malignant RCC; and (iv) allow more detailed studies defining the mechanism of alpha-IFN resistance and sensitivity in RCCs. The applicant has recently defined one kidney associated glycosylated differentiation antigen of 160 kilodaltons (gp160) whose cell surface expression strongly correlates with the resistance of RCCs to the anti-proliferative effects of alpha-IFN both in vitro and in vivo in a mouse model. Immunological analysis using anti-gp 160 mouse monoclonal antibodies shows that gp160 is normally constitutively expressed as a cell surface glycoprotein on cells of the glomerulus and proximal tubule portion of the human nephron, on 80% of cultured and noncultured RCCs, but is not present on a wide range of normal and neoplastic tissues of nonkidney origin. The precise molecular structure and function of gp160 and its role in IFN resistance is unknown. Preliminary analyses of gp160 positive, IFN-resistant and gp160 negative, IFN-sensitive RCCs to determine the mechanism of IFN sensitivity/resistance revealed similar numbers of high affinity cell surface IFN receptors in all RCCs. However, in contrast to gp160 negative IFN sensitive RCC cells, gp160 positive IFN resistant cells did not exhibit a down regulation of the epidermal growth factor receptor in response to alpha-IFN suggesting that alpha-IFN resistance in RCCs may in part be due to a defect in transcriptional activation. Therefore, the broad objectives of this research proposal are to characterize gp 160 and to identify other genetic elements relevant to the renal cell carcinoma phenotypes of IFN resistance or sensitivity. The specific aims are (i) to molecularly clone the genetic sequences encoding the kidney related differentiation antigen gp160 from renal cells, analyze its sequence, structure, and relatedness to other known proteins; (ii) to determine if the introduction of a complete cDNA copy of gp160 into alpha- IFN sensitive renal cancer cells confers an IFN resistant phenotype; and (iii) to examine alpha-IFN modulated gene expression in IFN resistant and IFN sensitive renal cancer cells, specifically interferon stimulated genes (ISGs) and interferon stimulated gene factors (ISGFs). Defining the role of specific proteins in the resistance (or sensitivity) to alpha-IFN will be a first step towards circumventing these mechanisms of resistance and the development of effective therapies.